Method for making and applying a bottle cap

ABSTRACT

The subject is a bottle cap of the type which is first pushed on, but thereafter may be twisted off and on. A shell is made from a cupped blank having a substantially straight skirt. The skirt is then knurled or fluted, the inside root diameter of the flutes being a close sliding fit on the crests of the bottle finish threads to which the cap is to be applied. When knurling, the rim of the skirt is curled inward slightly to an inside diameter about the same as the inner root diameter of the flutes. After inserting a suitable seal ring or disc, the shell is pushed down over the threaded finish of the bottle into sealing engagement with the lip. While so holding the cap, portions of the skirt are conformed to the thread formations on the bottle finish, thus providing a releasable threaded engagement. As the threads are formed in the skirt, the inwardly turned edge is closely conformed to the finish, in which position the edge is shielded against accidental contact by the fingers, when unscrewing the cap to open the bottle.

United States Patent 1 Moller [451 Dec. 5, 1972 I 1 METHOD FOR MAKINGAND 3,123,241 3/1964 Nofer et a1 ..215/39 APPLYING A BOTTLE CAP2,010,228 8/1935 Gibbs ..113/121 A 7 t l lnvem or Jens! Moller westmomPrzmary Examiner-Charles W. Lanham [73] Asslgneez Continental CanCompany, Inc., Assistant Examiner-Michael J. Kennan New York, NY.Attorney-George E. Szekely, Joseph E. Kerwin and 221 Filed: Dec. '18,1969 w'lham [21] Appl. N0.: 888,116 [57] ABSTRACT Related US.Application Data The subject is a bottle cap of the type which is firstpushed on, but thereafter may be twisted off and on. [62] E i 1968 Ashell is made from a cupped blank having a substantially straight skirt.The skirt is then knurled or fluted, 7 the inside root diameter of theflutes being a close Sliding fit on the crests of the bottle finishthreads to [58] i C A which the cap is to be applied. When knurling, therim le 0 can "'i' ii 4 of the skirt is curled inward slightly to aninside 3 44 diameter about the same as the inner root diameter of theflutes. After inserting a suitable seal ring or disc, 56 R f Ct d theshell is pushed down over the threaded finish of 1 e erences l e thebottle into sealing engagement with the lip. While UNITED STATES PATENTSso holding the cap, portions of the skirt are conformed to the threadformations on the bottle finish, thus 3,135,408 6/1964 St. Jacques..215/39 providing a releasable threaded engagemem AS the 876,361 1/1908Kraft et a1 "113/121 A threads are formed in the skirt, the inwardlyturned 3,517,848 6/1970 Kesler et a1 ..215/43 edge is closely conformedto the finish in which posh 3,219,004 11/1965 W11t011 ..113/121 A tionthe edge is Shielded against accidental Contact by 3,523,624 8/1970Curry ..215/39 the fingers, when unscrewing the p to p the 3,503,5343/1970 Moller ..2l5/39 2,302,542 11/1942 Gibbs ..113/121 AA 1,658,6032/1928 Kowal .l 13/121 A 4 Claims, 11 Drawing Figures 1,659,703 2/1928Ramsey ..113/121 A Q: 7 I I 33 l l H 1111 21. ii 1 i@1 18 b 1|| /WI "1\I I7 (Q R K K V I11 m1 111111 20 1'21 PKTENTEDIJEB 5 I972 SHEET 3 0F 4METHOD FOR MAKING AND APPLYING A BOTTLE CAP BACKGROUND OF THEINVENTION 1. Field of the Invention This invention relates to caps ofthe type primarily intended for sealing bottles of carbonated beverages,more particularly the type which can be applied and sealed in a mannersimilar to the conventional crowning procedures, but which maythereafter be unscrewed and used as a reclosure-in the manner of screwor lug caps.

2. The Prior Art In recent years, there has been an increasing demandfor beer and soft drinks large bottles, such as half quarts and quarts.This demand has been stimulated in large part by price and conveniencefactors. However, a major deterrent to wider acceptance of largerbottles for home consumption is possible wastage by virtue of unusedcontents losing carbonation and going flat.

Conventional crown caps cannot ordinarily be used as reclosures, sincethey are almost invariably spoiled in removing them. Various types ofreclosure stoppers, plugs, and caps have been brought on the market, buthave not met with substantial acceptance. Convenience is best served byproviding a reusable cap on each bottle, for example, a thread or lugcap. Such a cap is also desirable for'small bottles, not usuallyrequiring reclosure, to enable the user to remove the cap without abottle opener.

Tooling and equipment problems, particularly in the soft drink bottlingfield, generally require that press-on cap application be retained, tobe generally adaptable to crowning presses, or comparable equipment,which has been found most satisfactory and economical in the bottlingconditions involved. It has heretofore been proposed that caps be madeof substantially conventional crown form, in sizes to fit over a finishwith suitable thread formations and threaded in situ. However, theconventional crown cap entails a configuration in which the skirt isflared out, or at least substantially spaced from the bottle finish,with a sharp edge for engagement by prying bottle opener. A cap of thisbasic configuration does not lend itself to turning with the fingers,particularly because of the hazard in cutting fingers on the exposededge. Also, threaded closure quality and the characteristics obtainedwith conventional crown forming and crimping techniques have not beenfound entirely satisfactory. Various modifications and alternatives havebeen proposed to overcome the configuration with a suitable pry edge.Except for costlier varieties available only at premium prices, thecombination caps in general use are dangerous, in that the sharp pryedge is exposed to contact with the fingers of a user twisting the cap.

SUMMARY OF THE INVENTION It is an object of this invention to provide abottle cap for push-on application, with dependable twist-off removaland reclosure, which is simple and economical to manufacture and apply.

It is a further object of this invention to provide a cap of the generaltype designated which is producible with minimum material of ordinarycommercial quality, reliably conformable to simple thread-form finishes,and which can be applied thereto on substantially standard cappingmachines at high production rates.

It is a still further object of this invention to provide a cap of thegeneral class indicated, in which a shielded edge may be formed withoutextra material or extra operations as compared with conventional crowncaps of similar size and sealing requirements.

The foregoing and other objects and advantages derive from a novelformation and application of the cap, utilizing a cupped blank having astraight skirt so formed as to produce a shell with fluted or knurledskirt, the skirt retaining its generally straight character. In the samedie forming operation,- the skirt rim is coaxed inward to an edgediameter substantially congruent with the diameter at the knurl valleyswhich diameter is slightly larger than the bottle thread or lug crestdiameter. The finished cap, having a seal ring, disc, or gasket in theshell, is pushed down with force to compress the seal on the bottle lip.While the cap is several problems, but prior to this invention, no fullythus held, coacting die members form portions of the skirt upon thethread formations, seating the rim with its edge in shielded position ata diameter less than that of the knurl crests.

By virtue of the structure and procedure described, not only are the capthreads well formed and even, but a lead thread of substantial extent isformed through the rim, so that the cap can be unscrewed withoutdistorting the inturned rim. The cap can be easily retightened, withminimum cross-threading hazard, and without pounding or snap action.Thus, the cap operates after its initial application as a twist cap,assuring the advantages thereof in ease of removal and reclosure, withthe mechanical advantage of the thread or lug formations to effect atight seal upon reclosure. The knurling affords an excellent fingergrip, the crests acting to keep the fingers safely away from the sharprim edge.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 4 is a section similar to thesection of FIG. 2, showing the configuration of the shell afterwithdrawal from the tooling and upon insertion of the seal element;

FIG. 5 is a section through a portion of a bottle neck having a threadedfinish, showing the application of the cap of FIG. 4 with the cap heldin sealing position, just prior to actuation of the thread-forming diepart;

FIG. 6 is a section similar to that of FIG. 5 showing the fullyformedcap held in the crimping die,just prior to die retraction;

FIG. 7 is an elevation of a bottle top with a cap according to thisinvention applied thereto, a portion of the cap being broken away toshow the bottle thread formation;

FIG. 8 is a section similar to FIG. 1, taken through a modified cup,showing a skirt variation;

FIG. 9 is a section similar to FIG. 2, illustrating a different knurlingmethod, as applied to the cup shown in FIG. 8;

FIG. 10 is a horizontal section of Line 1010 of DESCRIPTION OF PREFERREDEMBODIMENT FIG. 1 shows the first stage in the preparation of the cap.At this stage, the shell blank 8 is a simple cup having a slightlycrowned top panel 10 and a straight cylindrical skirt 1 I, joined byradius 12. Such caps are readily mass-produced by blanking and formingin wellknown manner from metal strip of suitable analysis and temper,generally comparable to that used for conventional crowns.

FIG. 2 shows the configuration of the fully formed shell, seen asresting against the tool 13 at the completion of the knurl. Tool 13 is aroll, rail or segment, according to the type of equipment selected forthe operation. That is, the part may be clamped and tool 13 rolled aboutskirt II; the tool 13 may be held stationary and the part rolled againstthe working face; or tool 13 may oscillate as the part revolves on amandrel. In any case, the action being generally that of rolling, tool13 is hereafter referred to as a roll. The view is fragmentary, it beingunderstood that the part is symmetrical about the vertical axis. The rimof roll 13 is circumferentially undulated or ribbed, with the traversepeaks I4 tangent to a cylinder whose diameter is less than the outsidediameter of the shell blank skirt 1 1, whose maximum diameter iscontrolled by the undulation root diameter, at roots 15. When roll 13 ispressed and rolled against cylindrical shell shirt 11, the undulated orribbed surface forms corresponding undulations, flutes or knurling bydeformation of skirt 1 1, the resulting configuration being in effect astraight knurl. As best seen in FIG. 3, the resulting skirt contour isgenerally sinusoidal in cross-section, with peaks and valleys on theouter surface thereof constituting elements of cylinders, as determinedby the corresponding roll elements 14 and 15.

In a representative size, the desirable flute pitch angle is about 12,that is, there are about 30 flutes. Ample stiffening is effected withflute depth on the order of twice the thickness of a representativesuitable material, it being understood that the number of flutes mayvary according to the cap diameter, as well as thickness and temper ofthe material selected. In general, the cap made and applied according tothis invention has characteristics conducive to use of somewhat thinnermaterial than heretofore feasible in crown caps of comparable size.

Referring again to FIG. 2, the forming roll is provided with a bottomradius 16, blending outward from the undulation valleys 15, toward thepeaks 14. As skirt 11 is being knurled, the radius 16 coaxes edge 17inward, correspondingly forming the radiused, inturned .rim 18, which isvirtually wavele'ss at edge 17. The roll v13 is so contoured that thefinished diameter of edge 17 is substantially the same as diameter D,FIG. 3, resulting in a smooth blending of fluted skirt 11 into the rim18, free of raggedness or irregular formation, the skirt remaininggenerally straight.

A liner, gasket, or a sealing ring of substantially any type ordinarilyused with crown caps, may be readily adapted as a seal for use in thecap of this invention. FIG. 4 shows the cap of FIGS. 2 and 3 with apreferred liner 19, which has been found most suitable to theapplication and service conditions here involved. The design andperformance characteristics of the liner here shown, as they obtain inassociating with crown caps, are described in US. Pat. No. 3,127,920,issued to Henry .I. Dorn, June 8, I965.

FIGS. 5 and 6 show a preferred mode of applying the cap of FIG. 4 to thefinish of a typical bottle 20. The tooling shown fragmentarily is thatwhich is suitable for use in the crowning presses generally employed inoperations of the character involved. The bottle finish is provided withexterior thread formations 21. Form ations 21 are not necessarilycomplete turns, but may be merely elements of threads, or thread-formlugs. However, best results are obtained if formations 21 constitute theequivalentof about two-thread length. The threading may be single orcompound.

The cap 9 is pushed over the top of bottle 20, which is centered in diering 22, in turn centering cap 9 on bottle 20. Edge 17 and flute valleys32 closely telescope the thread formation 21. Punch 23 is brought downon cover panel 10 with sufficient pressure to seal liner 19 on lip 24,which pressure may, be established by spring-loading punch 23 in awell-known manner. Punch 23 is compounded with a follower ring 25,guided by punch 23 at the interface 26. In the stage of FIG. 5, follower25 is in partially retracted position.

Referring now to FIG. 6, the view is rotated one-half the fluting pitchfrom the view of FIG. 5, as indicated by section lines in FIG. 3. Whilepunch 23 holds cap 9 in sealing position, follower 25 advances towarddie 22 and cap 9. The die 22 is of the resiliently collapsible type,made of rubber, for example. The depth of die 22 is somewhat greaterthan the depth of cap 9, the tooling and part being so positioned thatthe top face 28 of die 22 is initially in or slightly above the plane ofcap cover panel 10, with cap 9 in its sealed position. Follower 25 has ashallow conical lead face 27, while collapsible die 22 is an annulus ofnormally rectangular cross-section. As ring 25 advances toward die 22,the leading face 27 first contacts die face 28, compressing ring 22,thereby setting up fluid pressure conditions characteristic or rubber ofother polymeric materials, with an intensified radially inward bias inconsequence of the component in that direction established by theconical face 27, which tends to crowd the die material inward anddistribute the deformation pressure uniformly around the circumferenceof die 22 as follower 25 advances. The pressure of die 22 against skirt11 and consequent flow of die material into flute valleys 32 causes thevalley walls 29 to press against the creasts of thread elements 21, withan accompanying collapsive effect, due to pressure above and below thethread creasts, forming interrupted female thread elements 30 in skirt11. The flute peaks 33, not being subject to the concentrated bentstresses, are substantially undistorted by the die pressure, assuringresistance to destructive collapse, and retaining the generally stiffcharacteristics of the fluted skirt 11. Also, the general stiffness ofskirt 11 is suff cient to minimize ovality or other irregular formationdue to imperfect distribution of constrictive pressure.

At the same time that die 22 forms the thread elements 30 in skirt- 11the pressure on inturned rim l8 collapses portions thereof inward alongthe lowermost bottle thread formation 21 against collar 31, the diameterwhereof is the same as, or slightly greater than, the root diameter ofthreads 21. Thus, the lowermost skirt thread formations extend into therim l8; constituting thread leads, while the edge 17 hugs the finishwithout general bending relative to the line of skirt 1 1, minimizingresidual stresses in skirt 11, and aiding retention of threadconformation in subsequent removal and reclosure.

The working stroke of follower 25 is so regulated as to assure thedisplacement of die 22 in the amount required for conforming the knurlroots of skirt 11 to threads 21. Overloading of the tool is prevented inthe usual manner, by suitable spring loading. Follower 25 is desirablyrelieved at 125 so that at maximum stroke relative to punch 23, follower25 will not strike panel 10, thus precluding bottoming and possiblemarring of cap 9. On completion of the follow stroke, cap skirt 11 isfully formed, locking cap 9 in sealed position on hot tle 20. Punch 23and follower 25 thereupon retract to positions of readiness foroperation upon the next bottle and cap presented. It will be understoodthat the tooling described may be incorporated in the usualmulti-station capping press for automatic, high-volume production.

The general configuration of the completed closure is best seen in FIG.7. As here shown, the finish has a triple thread formation 21, eachelement of which is somewhat more than one-third turn along the helix,

establishing an overlap whereby to provide two-thread engagement ofsubstantial arcuate extent in three sectors around the circumference ofthe finish. The arrangement assures ample grip with the cap in sealingposition, minimizes cocked engagement of the threads, and keeps threadfriction minimum when turning the cap free or tightening. Edge 17, beinginturned well inside the diameter of flute peaks 33, is fully guardedagainst finger contact when the user removesor replaces cap 9. Theknurled skirt surface provides an excellent non-slip finger grip.

The finish thread length is selected such that rim 18 of cap 9, whentight, lies with edge 17 in a horizontal plane through the threadtermini 121 of the lowermost thread formations 21, whereby thread leadsare formed through rim 18 when the cap 9 is applied as previouslydescribed. This provision assures easy starting for reclosure. In thecase of the usual beverage bottle top, a finish length of about l/4inch, a thread pitch of about 3/32 of an inch, and a helix angle ofabout 10 constitute a suitable thread formation, which in thethreeelement configuration shown provides a desirable quick-actingremoval and reclosure, with correspondingly short turn of the cap 9.With this thread dimensioning, the uppermost formation 21 startssomewhat below the lip 24, minimizingthe chipping, galling, andsplintering hazards which otherwise may obtain in a threaded glassfinish. The uppermost finish band 34 is held to a diameter about thesame as the thread root diameter, thus acting as a pilot for replacingthe cap. 7

The closure structure and proportions above described can be executed inusual bottle top sizes with a cap blank and total material requirementless than that involved with conventional crown caps, effectuatingexcellent economy in material costs, particularly as compared to designsheretofore proposed for push-on, twist-off caps of the class involved.

MODIFICATION The above described embodiment involves formation of theflutes and coaxed rim in a cylindrical skirt by means of a one-pieceroll. Knurling and coaxing of a slightly flared or coniform skirt isillustrated in FIGS. 8, 9 and 10, in which parts corresponding to thoseof FIGS. 1 through 5 are given like reference numerals with the additionof 100.

The blank 108 of FIG. 8 is similar to blank 8 of FIG.

- 1, having a top panel 110 and a skirt 1 11, connected by radius 112.However, in this case, the skirt 111 is slightly flared or coniform,downwardly and outwardly, being substantially a portion of a rightcircular cone, except that the narrow rim 118 is substantiallycylindrical. Thus, the rim 118 is bent slightly inwardly of a downwardextension of the main skirt portion 111.

As seen in FIGS. 9 and 10, the final forming tool assembly consists ofthree principal tools, a cap mandrel 150, a coaxing tool 151, and aknurling tool 152. Referring particularly to FIG. 10, the mandrel isprovided with equally spaced ribs 153, alternating with valleys 154 ofsubstantially the same circumferential extent in each case as thecorresponding rib 153. The valleys 154 are outwardly convex, on a circlecentered on the center of mandrel 150. That is, the roots 154 constitutearcs of a common circle concentric with mandrel 150. Knurling tool 152is a rail segment provided with ribs 155 and valleys 156 which arecomplementary to the formations of mandrel 150, so that the mandrel 150and roll'l52 can be loosely meshed as shown, with clearance for materialto be formed between them.

Skirt 111 is a loose fit over the mandrel 150. The crest diameter ofribs 153 at the base of the mandrel cone is smaller than the inside, orroot, diameter of the coaxed rim 118, at edge 117, so that the completedshell can be stripped from mandrel 150 without interference ordistortion of rim 118. A seen in FIG. 10, skirt 111 is knurledprogressively, being held to mandrel 150 by segment 152 along thatelement which is instantaneously in the working plane 161. The relief ofthe forming roots at 162 and 163 affords clearance to minimize jammingor seizing as the material is rolled and bent over the meshing ribs 153and 155.

FIG. 11 schematically illustrates a suitable tool setup in a rotarymachine arrangement. A number of vertical spindles 158 are mountedaround the periphery of a table 159, which is rotatably mounted on acolumn 160. Mandrels 150 are revolvably supported on spindles 158. Theknurling segment 152 and coaxing die 151 are concentric with table 159and are fixed in position for rolling mesh traverse of mandrels 150 astable 159 rotates, the relationship being as shown in FIG. 10. Thearcuate extents of the knurling and coaxing segments l52, 151 are suchthat each mandrel 150 makes at least one full revolution in traverse offull ribs 155, which drive the mandrel on spindle 158 as the skirt 11 1is knurled. The usual blend section is preferably incorporated in tools151, 152 to minimize chatter or jar at the beginning of the pass.Otherwise, sudden or irregular capture of the part may causemalformation and seizing. A shown in FIG. 9, ribs 155 may be relived attheir upper ends, along lines 164, to avoid fluting through the capradius 112, This results in a blend radius 165 between root 132 andradius 112, which latter is maintained around the cap.

The shell formed as shown in FIGS. 9 and may be completed in a mannersimilar to cap 9 of FIG. 4 and then applied to the bottle substantiallyas in FIGS. 5 and 6, in the manner previously described. It will also beapparent that the blank and tool combination of FIG. 2 may beimplemented as in FIG. 11 to produce shells 88 economically in quantity.

With either cap form, 9 or 109, the same salient advantages arerealized. The generally straight skirt, 11 or 111, can be readilyconstricted by essentially direct radial forces uniformly appliedagainst substantially the entire length and circumference at the skirt,as by the arrangement of FIGS. 5 and 6. A pressure sufficient to conformthe knurlroots to the finish threads will not, and need not, alter thegeneral configuration of the skirt, the flutes affording the stiffnessnecessary to prevent general distortion or localized malformation, whileproviding the controlled leverage and backing of sufficient magnitude tocause good thread formation in the knur] roots upon constriction.Because there is no sharp, general bending of skirt, such as requiredfor crimping the sharply flared skirt of conventional crown caps, thecap according to this invention is not subject to the strain failurescharacteristic in sharp bending of sheet metal. Hence, lighter weight,ductile material of less costly analysis and temper may be used, furtherfacilitating good thread formation and maintenance of shape forreclosure. Also, the skirt length for caps hereindescribed is generallyless than that required for conventional crimp closure, permitting asmaller cutedge diameter for the cap blank.

The slight skirt taper of the blank and shell in the form of FIGS. 8 and9 assists in preventing the skirt material from riding up the tool facesand holds the rim down on the coaxing die. The modified form has thesame advantageous characteristics as the cap of FIG. 4. The slightbending of the skirt relative to the top panel when constricting theskirt does not involve significant strain, being readily accommodated inthe top radius.

Where particular operations or tools are separately shown or describedherein, for example, formation of cups from strip, description in suchmanner is given only for the sake 'of clarity.

It will be understood that the various forming operations for either ofthe embodiments described are not necessarily performed in single stagesof independent machines, or stations, but are preferably integrated byuse of compound tools and automatic transfer devices in the manner wellknown in the tool and die art related to crowns, caps and similar smallparts generally.

It will also be understood that such terms as punch", die", roll andmandrel are used herein as seems most apt in describing a particulartool or part thereof, and not to infer that one or the other isnecessarily the moving part where relative motion of the several toolparts is indicated. Wherever the terms threads or thread formations areused herein, such terms are used as descriptive of the preferredembodiment, and not by way of limitation to particular such formationsshown, the invention being readily adaptable to camming lug finishes andother equivalent twist engagement means.

The foregoing descriptions of particular embodiments are given by way ofexample. Other forms, variations, and modifications may be devised bythose skilled in the art, following the teachings herein, withoutdeparting from the spirit of the invention and the scope of the appendedclaims.

What is claimed is:

l. A method of forming a cap having a top panel and a skirt adapted forconformation to external thread formations on the finish of a bottle orthe like, which method comprises:

a. blanking and forming sheetmaterial to form a cup having a generallystraight skirt;

b. knurling a principal lengthwise portion of said skirt bycircumferential bending deformation of said material for establishing acircumferential series of straight flutes in said skirt, whilemaintaining said skirt generally straight; and

c. coaxing the rim of said skirt radially inwardly of the major diameterof said flutes for constituting said cap with the edge of said skirtinwardly of the major diameter of said flutes in a generally straightskirt depending from said top panel.

2. A method of forming a cap according to claim 1, wherein said cupskirt is generally coniform, a narrow rim portion of said cup skirtbeing slightly inturned relative to the general line of said cup skirt,whereby to predispose said rim for said coaxing.

3. A method of closing a container mouth having ex- I ternal threadformations, the closure including a cap having a top panel and agenerally straight shirt, said skirt having a circumferential series ofaxial flutes along a substantial portion of the length of said skirt,said flutes being constituted by circumferential bending deformation ofsaid skirt, and said skirt having a rim terminating in an inturned edge,said method comprising the steps of:

a. holding said cap on said month with said skirt telescoped over saidthread formations; and applying substantially direct radial pressurealong and about substantially the entire length and circumference ofsaid skirt, of an intensity to effect constriction of said skirt,thereby conforming root elements of said flutes to said threadformations and collapsing said rim;

thereover, the intensity of said pressure being sufficient to conformportions of said rim to said thread formation portions for establishinglead thread formations in said rim.

1. A method of forming a cap having a top panel and a skirt adapted forconformation to external thread formations on the finish of a bottle orthe like, which method comprises: a. blanking and forming sheetmaterialto form a cup having a generally straight skirt; b. knurling a principallengthwise portion of said skirt by circumferential bending deformationof said material for establishing a circumferential series of straightflutes in said skirt, while maintaining said skirt generally straight;and c. coaxing the rim of said skirt radially inwardly of the majordiameter of said flutes for constituting said cap with the edge of saidskirt inwardly of the major diameter of said flutes in a generallystraight skirt depending from said top panel.
 2. A method of forming acap according to claim 1, wherein said cup skirt is generally coniform,a narrow rim portion of said cup skirt being slightly inturned relativeto the general line of said cup skirt, whereby to predispose said rimfor said coaxing.
 3. A method of closing a container mouth havingexternal thread formations, the closure including a cap having A toppanel and a generally straight shirt, said skirt having acircumferential series of axial flutes along a substantial portion ofthe length of said skirt, said flutes being constituted bycircumferential bending deformation of said skirt, and said skirt havinga rim terminating in an inturned edge, said method comprising the stepsof: a. holding said cap on said month with said skirt telescoped oversaid thread formations; and b. applying substantially direct radialpressure along and about substantially the entire length andcircumference of said skirt, of an intensity to effect constriction ofsaid skirt, thereby conforming root elements of said flutes to saidthread formations and collapsing said rim; whereby to constitute atwistably removable cap on said container, with said edge in protectedposition relative to fingers grasping said skirt to twist said cap.
 4. Amethod of closing a container mouth according to claim 3, wherein saidrim overlies portions of said thread formations when said cap istelescoped thereover, the intensity of said pressure being sufficient toconform portions of said rim to said thread formation portions forestablishing lead thread formations in said rim.